Delay activation/draw on GPU tile work completion

cc/raster/one_copy_raster_buffer_provider.cc

Index: cc/raster/one_copy_raster_buffer_provider.cc
diff --git a/cc/raster/one_copy_raster_buffer_provider.cc b/cc/raster/one_copy_raster_buffer_provider.cc
index 8b5acfc114f74491cced19aba7d862fbf9f9132b..10ac14ce446fce5494788129a877f3871c481d27 100644
--- a/cc/raster/one_copy_raster_buffer_provider.cc
+++ b/cc/raster/one_copy_raster_buffer_provider.cc
@@ -20,6 +20,7 @@
 #include "cc/resources/resource_util.h"
 #include "cc/resources/scoped_resource.h"
 #include "gpu/GLES2/gl2extchromium.h"
+#include "gpu/command_buffer/client/context_support.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "gpu/command_buffer/client/gpu_memory_buffer_manager.h"
 #include "ui/gfx/buffer_format_util.h"
@@ -161,6 +162,26 @@ bool OneCopyRasterBufferProvider::CanPartialRasterIntoProvidedResource() const {
   return false;
 }
 
+uint64_t OneCopyRasterBufferProvider::SetReadyToDrawCallback(
+    const ResourceProvider::ResourceIdArray& resource_ids,
+    const base::Callback<void(uint64_t)>& callback,
+    uint64_t pending_callback_id) const {
+  if (!async_worker_context_enabled_)
+    return 0;
+
+  gpu::SyncToken sync_token =
+      resource_provider_->GetSyncTokenForResources(resource_ids);
+  uint64_t callback_id = sync_token.release_count();
+  DCHECK_NE(callback_id, 0u);
+
+  if (callback_id != pending_callback_id) {

[vmpstr, 2016/12/07 21:00:25]

Can you add a comment explaining what's going on here?

+    compositor_context_provider_->ContextSupport()->SignalSyncToken(
+        sync_token, base::Bind(callback, callback_id));
+  }
+
+  return callback_id;
+}
+
 void OneCopyRasterBufferProvider::Shutdown() {
   staging_pool_.Shutdown();
   pending_raster_buffers_.clear();